Method of preparing high-density molded articles comprising cork and an elastomer



Patented Dec. 20, 1949 iJN-ITED STATES PIC-1E METHOD OF PREP RI HIGH-DENSITY MQLDED ARTICLES 'QOMRR N AND IAN ELA$T9MER .Robert tClayton, Jr., Cra-nford, J., assign or ,t t nda o lle rueet Qrurfinuekerrv ei ene i rlewa No D rawin'g. Application December 29, 1945,

Serial No."638,440 4 negat (ems-147.5)

This inventiompertainslto thepreparation of cork gaskets or slabsand particularly to gaskets and slabs prepared from. granulated.corkparticles with elastomer dispersions as thebinder.

At the present time cork gaskets or slabs with an elastomer binder ,are prepared by .the dry rubber techniquain, which a comparatively large volume of cork ismilledintoa very small volume of binder. The large difierenceinevolumeoft cork and binder used is due to the very low density of the cork. For example, in order to .prepare a gasket containingequalparts by weight .of cork and rubber binder, itisnecessary to incorporate .about twelve volumes of cork. into each ,volume of rubber. A very considerable amount of milling .or banburying' must be done in .order, toiblend the two components. Thisisnot onlytimeeconsuming but also expensive,,,and, in thelongmilling period, the cork is broken upnsoflthat theparticle sizetof the corkis-not uniform which inturn makes it diiiicult'if, not impossible, to meet speci- A much more practical, method, is to uselaldis persion or latex of the, ,e1 astomer ,asbinder. In

this way the binder maybe rapidlyincorporated ,into the mass of ,cork particlesin, for-example, a ,kneader. Furthermore, the cork particles arenot broken down because of, the lubricating ,efiectof the water and dispersingagentsend becauseof the short kneading time required. sHoweyer, when this mass is dried and then placedina mold, it was found that it could nottbesufficient- ,lycompressed in the usual molding equipmentand that accordingly the molded product was incapable. of. meeting specifications.

,It is the object of, this inyentionttoproyide;the art witha novel methodof preparing cork gaskets and slabs from granular cork particles and elas ,tomer dispersions as thebinder.

It is also the object of this inventiontoprerpare cork gaskets and, slabs which-are easily capabl f m in ificati n ,fro ranula cork particles and elastomersdisper sionserlatices.

These and other objectswill appear more clear- 51 m the d a esii ceiio a cla mswh e follow:

It has now been foundthat cork,.- l$kets,, a 1d the ordinary molding operation: "Them;

ing of the dried-batch is accomplished by sofew passes through the mill that the objections .of time-consumption and cork particle disintegrati'on mentioned above'in connection with the dry rubber technique are not encountered.

The elasto'mer dispersions orlatices which may be use djas a binder for cork granulesin' accordance with the present invention include natural rubber latex and the artificial latices obtained by 'polyrneriiiiig in aqueous "emulsions a' conjugated "diolefin "such 'as butadiene, isoprerie, piperylene or dimethylb utadiene or mixtures of such dienes or mixtures 'oflone or'mo're of said di'enes with one or mbre unsaturated comonomers such as styrene, si' bstituted st'yrenes such as methyl-,

ethyl orchloro-styrenes, acrylonitrile, methacrylonitrilefacrylic acid esters such as methyl acrylate and "methylmethacrylate; fuma'ric acid esters such as ethy1 fumarate and"unsaturated ketones 'such' as methyl vinyl ketone, methyl isopropenyl ketone and the like. While these latices may be used as ordinarily obtained or prepared,

l ith? i.;e., containing from about 20-30% of elastomer jso'lidsjlit ispreferred to utilize creamed latices containing at least about 45% of rubber solids.

The preparation of creamed synthetic rubber latices is disclosed in Serial No. 556,659, filed september 30,

I 1944, by Erying Arundale, now U. S. PatentNo. 2,444,801Q V l Theffollowing i'sgiven as an example of the preparation 'f'f'a'cork gasket stock inaccordance with the "present invention.

An, emulsioncopclymer of butadiene and, acryl difi'itrile'theratio'of "14 'parts of thefo'rmer to jzt'iiparts of the latter which "had been creamed :to f5l rubber solidswas compounded according tot he' following recipe, the parts being by weight:

r29 1 art n rit ieif e i e r ir e rm redi t w rm bar-ei P granulated cork (2O 30,:mefsh) in a kneader. The cork was jthoroiighly warped with the il'atexflcompounizi b'y uh, in tlje lineader. The batchwas 11 a s "q ere is a an satisf e t mi 3 massing on a friction mill. The massing could have been effected as well at even speed, i. e. on a calender. The millmassed product is obtained as a thin sheet and may be built up to any desired thickness. Several layers of mill massed sheets (in this particular case, in. thick each) were easily compressed in a cork mold at 250-500 p. s. i. pressure and to 1 inch thickness and cured while still in the mold under pressure in an air oven for 2 hours at 280 F. The slab was removed from the mold and it was found that the sheet had flowed together with no signs of laminations. The resultant gasket material was sub- 1 jected to a number of tests, the results of which are tabulated below:

Specific gravity 1.00 Per cent volume increase after 48 hrs.

100 C. in 10-c. transformer oil 9.9 Per cent compression after one minute loading 300 p. s. i 10.1 Tensile strength in p. s. i 622 preferred because of its speed of cure and for specific applications because of its oil resistance. Speed of cure is desirable because of the poor heat conductivity of the cork particles. However, in lieu of using butadiene-acrylonitrile latices or latex creams, the other synthetic rubberlike materials disclosed above may be used. The particular latex compounding ingredients utilized may be varied as desired.

Ordinarily about equal quantities (by weight) of rubber solids and cork are utilized for the production of gaskets in accordance with the present invention. Smaller or larger amounts of rubber solids may be used, however, depending upon the particular purposes for which the gaskets or sheets are to be used.

It may be seen therefore that I have provided the art with a novel method of preparing gasket materials easily capable of meeting specifications, particularly as to density, without destruction of cork particle size by the expedient of mill massing the cork-rubber composition prior to molding.

The foregoing description contains a limited number of embodiments of the present invention. It will be understood, however, that this invention is not limited to the specific conditions disclosed but may be varied without departing from the scope of the present invention as defined in the following claims.

What I claim and desire to secure by Letters 7 Patent is:

1. The method of preparing high density molded cork articles which comprises mixing granular cork particles with an aqueous elastomer dispersion, drying the mixture, subjecting insufiicient to break down the cork and curing the mill massed product.

3. The method of preparing high density molded cork articles which comprises mixing granular cork particles with an aqueous elastomer dispersion containing at least 45% of elastomer solids, drying the mixture, subjecting the dried mixture to mill massing in the absence of any additional elastomer and curing the mill massed product.

4. The method of preparing high density molded cork articles which comprises mixing granular cork particles with an aqueous elastomer dispersion containing at least 45% of elastomer solids, drying the mixture, subjecting the dried mixture to mill massing in the absence of any additional elastomer by passing the mixture through a rubber mill for a number of times insuificient to break down the cork and curing the mill massed product.

5. The process as defined in claim 1 wherein the elastomer dispersion is obtained by the polymerization of a conjugated diolefin of from four to six carbon atoms per molecule in aqueous emulsion.

6. The process as defined in claim 2 wherein the elastomer dispersion is obtained by the polymerization of a conjugated diolefin of from four to six carbon atoms per molecule in aqueous emulsion.

7. The process as defined in claim 1 wherein the elastomer dispersion is obtained by the copolymerization of a conjugated diolefin of from four to six carbon atoms per molecule and an unsaturated comonomer in aqueous emulsion.

8. The process as defined in claim 2 wherein the elastomer dispersion is obtained by the copolymerization of a conjugated diolefin of from four to six carbon atoms per molecule and an unsaturated comonomer in aqueous emulsion.

9. The method of preparing high density molded cork articles which comprises mixing ,granular cork particles with about an equal weight of elastomer in the form of a latex compound obtained by polymerizing a mixture of a conjugated diolefin of from four to six carbon atoms per molecule and acrylonitrile in aqueous emulsion, drying the mixture, subjecting the dried mixture to mill massing in the absence of any additional elastomer and curing the mill massed product.

10. The method of preparing high density molded cork articles which comprises mixing granular cork particles with about an equal weight of elastomer in the form of a latex compound obtained by polymerizing a mixture of a conjugated diolefin of from four to six carbon atoms per molecule and acrylonitrile in aqueous emulsion, drying the mixture, subjecting the dried mixture to mill massing in the absence of any additional elastomer by passing the mixture several times through a rubber mill and curing the mill massed product.

11. The method of preparing high density molded cork articles which comprises mixing granular cork particles with about an equal weight of elastomer in the form of a latex compound obtained by polymerizing a mixture of a conjugated diolefin of from four to six carbon atoms per molecule and acrylonitrile in aqueous emulsion, and creaming to at least 45% rubber solids content, drying the mixture, subjecting the dried mixture to mill massing in the absence of additional elastomer and curing the mill massed products 1 B! U 12. The method of preparing high density molded cork articles which comprises mixing granular cork particles with about an equal amount of elastomer in sulfur-containing latex form obtained by polymerizing a mixture of a conjugated diolefin of from four to six carbon atoms per molecule and acrylonitrile in aqueous emulsion, and creaming to at least 45% elastomer solids content and dispersing sulfur therein, drying the mixture, subjecting the dried mixture to mill massing by passing the mixture through a rubber mill for a number of times insufiicient to break down the cork and curing the mill massed product.

13. The method of preparing high density molded cork articles which comprises mixing granular cork particles with an aqueous elastomer dispersion, drying the mixture, subjecting the dried mixture to mill massing by passing the mixture through a rubber mill for a number of times insuificient to break down the cork, superposing several thin sheets obtained from the mill massing and curing the superposed sheets to form a non-laminated product having a density of at least 1.0 and which consists of about equal weights of cork and elastomer.

14. The method of preparing high density REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 647,112 Pearson Apr. 10, 1900 1,184,306 Bentley May 23, 1916 2,087,942 West July 27, 1937 2,250,987 Dunbar July 29, 1941 2,333,403 Youker Nov. 2, 1943 2,339,458 Champney Jan.. 18, 1944 OTHER REFERENCES Hill: Cork-rubber materials, Product Engineering, June 1939. 

